In the case of Wirtz, Secretary of Labor v. Local 153, Glass Bottle Blowers Association of the United States and Canada, AFL-CIO (1967), the U.S. Supreme Court ruled that labor unions are subject to regulation under federal law when they operate welfare funds for their members. The court held that such funds constitute a business activity affecting commerce and thus fall within Congress's regulatory power under the Commerce Clause of the Constitution. This decision was significant because it expanded federal oversight over union activities beyond collective bargaining and strikes to include benefits administration as well.

In the dissenting opinion for Wirtz v. Local 153, Glass Bottle Blowers Association, Justice Douglas argued that the majority's interpretation of "in commerce" was too broad and inconsistent with previous rulings. He contended that Congress intended to regulate only those activities directly involved in interstate commerce under the Fair Labor Standards Act (FLSA). In this case, he believed that employees engaged in internal plant maintenance were not sufficiently connected to interstate commerce to warrant federal regulation. Furthermore, he expressed concern about potential overreach by federal authorities into areas traditionally governed by state labor laws if such a broad interpretation of "commerce" was accepted. Thus, according to Justice Douglas' dissenting view, these workers should have been excluded from FLSA protections because their work did not constitute engagement 'in commerce'.